1. Field of the Invention
This invention relates to a frictionless supporting apparatus, more particularly to such an apparatus for movably supporting a working table which may be used, for example, in a vacuum chamber of an electron beam exposure installation.
2. Description of the Prior Art
Electron beam exposure installations have vacuum chambers within which are disposed working tables movable in a horizontal X- and horizontal Y-direction. These "X-Y tables" carry samples to be treated, such as wafers of semiconductors. Electron beams are suitably scanned or deflected onto the surface of the samples, while X-Y tables are contunuously moved.
Many proposals have been made for moving the working table in the X- and Y-directions with respect to a stage base. Well known among these is a step-and-repeat system. This system includes frame members having V-shaped guide grooves and bearings. The frame members move along the guide grooves, while the working table is repeatedly moved by steps in X- and Y-directions by a suitable actuator.
Also well known is a block guide system. This system includes blocks rigidly situated on a stationary base. The working table is provided with guide grooves for the above-mentioned blocks. The working table can be moved in the X- and Y-directions along the guide grooves.
The apparatuses for moving X-Y working tables according to such systems, however, have serious disadvantages. For example, it is difficult to smoothly move the working table at a high speed and in a precise step-and-repeat manner because of the large frictional coefficient between the V-shaped guide grooves and bearings or between the blocks and guide grooves formed in the working table. This leads to problems of reliability and durability, especially serious since the working table has to be moved in a vacuum chamber.
In order to solve these problems, proposals have been made for frictionless supporting apparatuses adapted for use in a vacuum chamber of an electron beam exposure installation. These include gas injection systems for floating and frictionless supporting a working table while it is moved in the X- and Y-directions. Such systems have many advantages, for example, high reliability and substantially permanent durability. The apparatuses for such systems, however, require precisely machined parts, which increases the apparatus costs. The apparatuses are also large in size and require high running costs due to the large amount of gas, such as air or nitrogen (N.sub.2), used in frictionlessly supporting the working table.